Folding machine controller



Oct. 27, 1964 E. M CLAIN FOLDING MACHINE CONTROLLER 2 Sheets-Sheet 1 Filed Oct. 12, 1961 //V V/V TOR Ed ward L. Me Ola/n A TTORNEY Oct. '27, 1964 E. M CLAIN FOLDING MACHINE CONTROLLER 7 Filed Oct. 12, 1961 2 Sheets-Sheet 2 //V VE/V TOR Edward L. McClain N mkamt A TTOR/VEY United States Patent 3,154,726 FOLDING MACHENE CONTRQLLER Edward L. McClain, Chicago, iii, assignor to Super laundry Machinery Company, (Chicago, lill., a corporation of Illinois Filed Oct. 12., 19611, Ser. No. 144,633 13 Claims. (Cl. 317-142) This invention relates to apparatus for controlling folding machines such as those employed by commercial laundries for folding bed sheets, table covers and similar flatwork articles. More particularly, the present invention is directed to logical circuitry for actuating an article folding means at the proper time in relation to the length of the article being folded and to its speed.

It is an object of this invention to provide an improved control device for programming the operation of a folding machine which, in comparison with prior art control systems, enables the folding of both long and short articles to be accomplished with greater accuracy and minimum operator attention, substantially increases the piece rate capacity of existing folding machines, and permits the use of much smaller machines in attaining a given throughput.

The construction and principles of operation of commercial folding machines are well-known and require little elaboration here. A typical folding machine employs an endless conveyor belt, generally having the form of a plurality of laterally spaced parallel ribbons or tapes, which moves the article to be folded across an article length measuring station and thence across a first folding means which may comprise a folding blade or an air blast means. On the basis of information received from the article length measuring station, the folding machine control device actuates the folding means when the midlength of the article moves into alignment therewith. The folding means then directs the article, at its midlength, into gripping engagement with a set of first folding rolls to effect a first fold of the article. If it is desired to fold the article a second time, this process is repeated again on the once-folded article by means of a second folding means and second folding rolls located farther along the roll train.

The successful operation of folding machines of the class described depends to a very great extent on the ability of the control device to locate accurately the midlengths of articles of dilferent lengths. To achieve this objective, numerous types of control apparatus have been suggested by the prior art including rather complex assemblies of mechanical elements such as moving meas uring stations, dual speed folding machine driving motors interlocked with a timing means, and the like. None of these more complicated systems has met with any widespread acceptance by the laundry industry.

One of the more popular types of control apparatus currently in use comprises a dual speed timer and a single article length measuring station, e.g. a feeler or finger switch, disposed a fixed distance ahead of the first folding means. When the leading edge of the article contacts the feeler switch, the timer commences its slow speed cycle and when the trailing edge of the article subsequently passes beyond the feeler switch thereby releasing it, the timer shifts over into its high speed cycle. The slow and high speed periods of the timer are so related to the speed of the conveyor means and the distance between the feeler switch and the folding means that the high speed period runs out when the midlength of the article has arrived at a point opposite the folding means, which event is utilized to cause actuation thereof. A second dual speed timer, connected in parallel or cascaded with the first, may be employed to actuate a second folding means to effect a second fold of the article. Although this system has heretofore enjoyed considerable popuice larity throughout the industry, it suffers several inherent disadvantages.

In the first place, it is desirable with any folding machine control system that at least the leading one-half of the article be engaged by the feed ribbons and be accelerated up to ribbon speed before the slow speed timing cycle is commenced, since any slippage between article and ribbons which might otherwise occur would result in substantial folding error; furthermore, it is necessary that the distance from the measuring station to the folding means be at least one-half the length of the longest piece to be folded. As above noted, conventional systems initiate their slow speed timing cycle when the leading edge of the article crosses the measuring station, at which time the leading one-half of the article, at least, must also be in coextensive contact with the feed ribbons ahead of the measuring station in order that no slippage error can be introduced. These conditions require that the total length of the feed section, e.g. both that portion thereof between the folding means and the measuring station and that portion thereof ahead of the measuring station, be at least twice the length of the longest article to be folded. As a consequence, the feed section of present-day folding machines is unduly elongated whereby additional ribbons and elaborate configurations of vertically stacked approach rolls, etc., are required, all of which contribute to increased capital investment of the user both in respect of machine cost and space cost, to say nothing of extra maintenance expense.

Secondly, in any control system utilizing a timing means, the accuracy of fold is almost exclusively dependent upon the accuracy of the timer since the delay time of the various mechanical elements is substantially constant and may be readily compensated for; the absolute timing error in turn increases as the total duration of the timing cycleincluding both the slow and high speed periods-increases. Therefore, the longer the timer runs, the greater the absolute folding error for a specified timing error. In the case of the single measuring station control system of the prior art, the total duration of the timing cycle or rundown period extends from the instant that the leading edge of the article crosses the measuring station to the moment that the midlength of the article arrives at the folding means; it can be demonstrated that the total duration of the timing cycle in such case is given by:

where D=distance between measuring station and folding means v=velocity of the article L=length of article between limits of zero and 2D.

The total timing interval therefore ranges from to 2 v v as L varies from zero to 2D, respectively. The absolute folding error correspondingly increases although the relative folding error (absolute error divided by article length) naturally decreases. The inherent result is that the relative folding error is greater for short pieces than for long pieces and even in the case of long pieces tends to be unsatisfactorily large. The prior art recognizes this problem and has proposed various solutions to accommodate short pieces. For example, it is suggested to reduce D by employing a second or short piece article measuring station positioned closer to the folding means than the long piece article measuring station, and to reduce ribbon velocity v in proportion by employing a 2-speed conveyor drive motor; or, alternatively, let v remain constant and employ a second timing means having a proportionately shorter rundown period. In either case manual switching means must be provided for selecting one or the other of the measuring stations, and continual attention by the operator and exercise of his judgment is required as to which of the measuring stations to select, a task which becomes very difficult in the high volume folding of articles of widely varying lengths. Furthermore, the additional apparatus and increased capital investment involved have not made this solution economically attractive to the industry.

Thirdly, the single measuring station control system of the prior art seriously limits the capacity of the folding machine to which it is adapted; that is, for all articles of length L less than 2D where D is the distance between the measuring station and the folding means, there is a minimum spacing which must be observed between successive articles. Since the slow timing cycle for a succeeding article must not commence until after the timer rundown period for the immediately preceding article has expired and the timer has been reset, the minimum spacing between articles is given by:

where L=length of article presently being folded.

In order to overcome this limitation, it is conventional practice to employ anywhere from two to as many as four independent dual speed timing mechanisms controlled by a stepping switch or flip-flop counter. When the first timer shifts from slow to high speed, it is then disconnected from the measuring station and the second timer is connected thereto whereby a succeeding article may be immediately measured without having to wait until the first timer has been reset. If the lengths of the articles are so short that the first timing period is still continuing when the second article is about to clear the measuring station, then a third timing mechanism must be provided if a third article is immediately to be measured. Although workable, such a complex assemblage of apparatus often entails considerable expense and repair problems.

The present invention overcomes to a substantial extent the above-noted deficiencies of present control systems. Briefly stated, the instant apparatus employs a dual-speed timing means and a pair of article presence sensors which are spaced apart a fixed distance ahead of the folding means. Both of the article presence sensors cooperate in the measurement of each article, whether it be long or short. The heart of the invention lies in a novel combination of logical gating or switching elements, the state of which is responsive to the sequence in which said sensors are activated and deactivated, and which in turn determines when the slow and high speed timing cycles of the timing means shall be initiated.

A. broad embodiment of this invention provides apparatus for locating the midlength of an article moving at constant velocity in a direction parallel to its length which comprises in combination: a forward article presence sensor and a rear article presence sensor, each of which sensors is activated so long as said article overlaps a corresponding fixed sensing point and is otherwise deactivated, said sensing points being spaced from each other in the direction of movement of said article, a dual speed timing means having a slow timing cycle and a fast timing cycle, a first gating means initiating said slow timing cycle in response to initial activation of said forward sensor and subsequent occurrence of either of two events consisting of (a) deactivation of said forward sensor and (1)) activation of said rear sensor, a second gating means initiating said fast timing cycle in response conjunctively to initial activation of said forward sensor and subsequent occurrence of both the deactivation of said forward sensor and the activation of said rear sensor,

Z1 and an output switching element operatively connected to said timing means and changing state upon termination of its timing period.

A more specific embodiment of this invention is directed to apparatus of the class described which comprises forward and rear article presence sensors, a dual speed timing means having a slow timing cycle and a fast timing cycle, a measuring cycle enabling gate, a timer enabling storage element responsive to deactivation of said enabling gate and activation of said forward sensor, a slow time cycle initiating gate responsive to activation of said timer enabling storage element and subsequent occurrence of either of two events consisting of (a) deactivation of said forward sensor and (b) activation of said rear sensor, a fast time cycle initiating gate responsive conjunctively to activation of said timer enabling storage element and subsequent occurrence of both the deactivation of said forward sensor and the activation of said rear sensor, said measuring cycle enabling gate being activated-by said timing means upon termination of its timing period.

It will be desirable at this juncture to define several of the terms appearing in the specification and claims in order properly to set forth what is considered to be the substance of the present invention. The term article presence sensor connotes any proximity detecting means having at least two logical states or levels of energization which are determined in accordance with whether or not an object happens to overlap a fixed reference point or article presence sensing point. Exemplary article presence sensors include, but are not limited to, photoelectric switches, pressure-sensitive switches, capacitance probes and radioactivity probes.

The article presence sensing poin is that point along the path of travel of the article at which the corresponding article presence sensor will change state because of the arrival or departure of the article to or from such point. Where the sensor is a pressure-sensitive or contact switch operated by physical contact with the article, its sensing point will obviously be identical with the location of such switch; however, where the sensor is a remote proximity detecting means such as a photoelectric switch responsive to the interruption of a light beam, the location of its sensing point relative to the article folding means may be and usually is different from that of the sensor. i e

The forward article presence sensor is the one whose sensing point is the more remote from the folding means, and the rear article presence sensor is the one whose sensing point is the closer to the folding means.

7 The term activation connotes the change of state of a circuit element or combination of elements from its normal or quiescent state to another or activated state having logical significance, whereas the term deactivationfconnotes the return of such element or elements from its activated state to its normal state. The fact that an element is activated or deactivated does not necessarily mean that it is energized or not-in the sense that an electric current is drawn thereby-since elements are commonly normally energized or normally de-energized.

The gating means is defined as a logical element or combination of logical elements which when activated, i.e., all .input conditions satisfied, permits some other circuit component to be activated either presently or subsequently. The gating means may comprise a switch or relay contact, apair of contacts in series or in parallel, or three or more contacts connected in series, parallel, or in various series-parallel combinations to furnish the desired logic; the gating means may comprise one or more memory gates which remain activated after subsequent removal of one or more necessary inputs (latching relay or flip flop) or may comprise a simple gate requiring continued existence of necessary input conditions in order that its activation be maintained. Although it is preferred to construct the logical circuitry of this inven- 3 e9 tion with mechanical switching elements for reasons of minimum cost and easy maintenance, it is recognized that equivalent circuitry may be assembled from vacuum tube or solid state logical elements such as flip flops, diode AND gates, diode OR gates, transistor gates, inverter gates, and the like. Therefore, it is intended that th term gating means include relay, vacuum tube and solid state logical elements.

Unlike conventional control systems employing a single article measuring station or sensing point, the slow timing cycle of the present invention does not commence with the activation of the forward sensor by the leading edge of an article. Rather, such activation of the forward sensor prepares the logic circuit to select and initiate the proper timing cycleslow or fastin accordance with any one of three possible subsequent events which must occur depending upon whether the article is short (its length is less than the distance between the rear and forward sensing points) or long (its length is greater than the distance between the rear and forward sensing points) or of intermediate length equal to the distance between rear and forward sensing points. If the article is short, the next subsequent event is the deactivation of the forward sensor when the trailing edge of the article crosses its sensing point; if the article is long, the next subsequent event is the activation of the rear sensor when the leading edge of the article passes its sensing point; if the article is of intermediate length, the next subsequent event is the simultaneous deactivation of the forward sensor and activation of the rear sensor. The logic circuit includes a first gating means which is activated in response either to activation of the rear sensor or to activation and subsequent deactivation of the forward sensor, said first gating means initiating the slow timing cycle of the timing means. In the case of a short article, the slow timing cycle therefore begins only when the trailing edge thereof passes the forward sensing point; in the case of a long article, the slow timing cycle commences when the leading edge of the article arrives at the rear sensing point. The logic circuit further includes a second gating means which is activated in response conjunctively to the initial activation of the forward sensor and to the subsequent deactivation of the forward sensor and activation of the rear sensor, said second gating means initiating the fast timing cycle of the timing means. In the case of a short article, the fast timing cycle begins when the leading edge thereof arrives at the rear sensing point; in the case of a long article, the fast timing cycle commences when the trailing edge thereof passes the forward sensing point. For an article of intermediate length equal to the distance between rear and forward sensing points, only the second gating means is activated and the timing means starts forthwith in its fast timing cycle when the trailing edge of the article passes the forward sensing point, the leading edge thereof simultaneously arriving at the rear sensing point. The rundown period of the tming means is adjusted such that the midlength of an article of length equal to twice the distance between rear and forward sensing points will be approximately opposite the folding means when the rundown period expires. The fast speed rundown period is one-half the duration of the slow speed rundown period. Actually, the rundown period is set to expire when the midlength of an article is still slightly ahead of the folding means in order to compensate for the time lag of the latter. An output switching element connected to the timing means is activated upon expiration of the rundown period, thereby providing a signal or contact closure for actuating the folding means.

It will be observed that the instant apparatus can accommodate articles having lengths ranging from slightly greater than zero up to twice the distance between rear and forward sensing points. Since neither the slow nor the fast timing cycle is commenced until the trailing edge of a short or intermediate article has passed the forward sensing point, at which time the article is wholly engaged by the feed ribbons and has been accelerated to uniform velocity so that no slippage error can occur, the additional length of approach or acceleration zone ahead of the article measuring station required of folding machines controlled by conventional systems can be eliminated. In other words, the article feed and acceleration zone is coextensive with the measuring zone with the result that the total length of the feed ribbons ahead of the folding means may be reduced by 50% as against machines controlled by conventional systems, without reducing the maximum length of an article which can be folded. Even in the case of a long article, the slow timing cycle does not commence until the leading edge of the article reaches the rear sensing point, by which time at least one-half of the article has become engaged by the feed ribbons which is sufficient to negative the possibility of slippage.

A second advantage of this invention resides in the fact that the total duration of the timing period, including both slow and high speed timing cycles, is always less than the comparable timing duration of conventional control apparatus utilizing a single sensing point, whether the article be short or long; this means that the timing error inherent in all timers, whether mechanical or electronic, will produce less folding error than the single sens ing point system of the prior art, all other variables being equal.

A third and very substantial advantage provided by a preferred embodiment of the present invention is the reduction of the minimum spacing required to be observed between successive articles. It has previously been shown that the minimum spacing required of a single sensing point apparatus is given by:

dms D -2 Where D is the distance between sensing point and folding means, and L is the length of the piece presently being folded. In other words, one must wait until the present folding operation is at least begun and the timer reset before the leading edge of the next succeeding article can be permitted to pass the sensing point. Such limitation is largely obviated by a preferred embodiment of the invention whereby, following the deactivation of the forward sensor incident to the trailing edge of a first article passing the forward sensing point, the forward sensor may immediately thereafter be activated by the leading edge of a second article in line without disturbing the timing period for the first article; the second article may therefore have moved well into the article measuring zone before the first article is folded. The only limitation which must be observed is that the folding of the first article he initiated and the timing means be reset before the trailing edge of the second article passes the forward sensing point. It follows that the minimum spacing between successive articles for the dual sensing point apparatus of this invention is given by:

where D is the distance between rear and forward sensing points, L is the length of a first article presently to be folded, and L is the length of a second article immediately following. It is apparent that the minimum spacing is reduced by the length of the next succeeding article. Frequently, the lengths of the first and/or second nth articles in a line may be such that the minimum spacing is nearly zero; this is never possible with a single sensing point control apparatus except in the unlikely event that the articles are of maximum length equal to 2D. In any case, the present invention permits the capacity of a given folding machine to be materially increased by reducing the minimum spacing requirement and without having to employ a plurality of cascaded timing mechanisms as has heretofore been customary.

The construction and operating principles of this invention, together with particular embodiments and refinements thereof, may best be described in conjunction with the accompanying drawings, to which reference may now be had. It is intended that the drawings are merely illustrative of the best mode of practicing the invention and are not to be interpreted as delimiting more than its essence.

FIGURE 1 is a sectional elevation view of a typical folding machine and also illustrates diagrammatically the principal components of the present control system and their manner of connection with said machine.

FIGURE 2 is a schematic circuit diagram of the logic elements and timing means of the invention.

With reference now to FIGURE 1, there is shown in elevation a conventional laundry folding machine indi cated generally at lltl. This view of such machine is of course considerably simplified, and only so much of the detail thereof is presented as will aid in a clear understanding of the control apparatus itself. A feed conveyer belt Ill, which may comprise a plurality of laterally spaced ribbons, moves a flatwork article 12 of length L from right to left at constant speed toward the folding rolls. The first folding means comprises a pivoted folding blade 14 which is moveable by air piston 13 upwardly through the spaces between feed ribbons 11. The second folding means comprises a pivoted folding blade 18 which is moveable by air piston 17 upwardly through the spaces between ribbons 15. Consider first the control system for the first folding means. A stationary light source 21 projects its beam downwardly between a pair of feed ribbons llll onto mirror 22 which reflects the light beam back to photoelectric cell 23. Cell 23 is connected by line 27 to the grid circuit of photoelectric amplifier 28. A relay 29 has its coil connected in the plate circuit of amplifier 28; the contacts of relay 29 form part of the logic section of controller 30, as hereinafter explained. Cell 23, amplifier Z8 and relay 29 together comprise the forward article presence sensor of the invention. As long as cell 23 receives the light beam, relay 29 is energized and the forward sensor is said to be deactivated. When an object such as article 12. interrupts the light beam, relay 29 is de-energized and the forward sensor is said to be activated. In like manner, a stationary light source 24 projects its beam downwardly between a pair of feed ribbons 11 onto mirror 25 which reflects the light beam back to photoelectric cell 26. Cell 26 is connected by line 31 to the grid circuit of photoelectric amplifier 32. A relay 33 has its coil connected in the plate circuit of amplifier 32; the contacts of relay 33 form part of the logic section of controller 30, as hereinafter explained. Cell 26, amplifier 32 and relay 33 together comprise the rear article presence sensor of the invention. The point at which the reflected light beam received by photoelectric cell 23 intersects the path of travel of an article is the forward sensing point, indicated by point A; the point at which the reflected light beam received by cell 26 intersects the path of travel of the article is the rear sensing point, indicated by point B. The distance D between points A and B fixes the maximum length of an article which can be folded, namely, twice the distance D. To effect a first fold, the operation of controller 30 is such that when the midlength of article 12 arrives at a point just slightly ahead of folding blade 14, indicated by point C, a contact closure in controller 30 opens solenoid air valve 42 to admit compressed air to piston 13 through line 43; air piston 13 moves folding blade 14 upwardly td direct the midlength of the article into gripping engagement with folding ribbons 15 and 16.

The second fold of the article is accomplished in much the same manner. The forward sensor for the second folding means comprises light source 34, mirror 35 and photoelectric cell 36; the rear sensor for the second folding means comprises light source 37, mirror 38, and photoelectric cell 39. Cells 36 and 39 are connected by lines 40 and 41, respectively, to a similar control apparatus such as that shown for the first folding means (omitted here to avoid repetition). The second fold controller will actuate air piston 17 and folding blade 18 when the midlength of the once-folded article is carried by ribbons 15 into vertical alignment with plate 18, whereupon the once-folded article will be directed upwardly into gripping engagement with folding ribbons 16 and 19. The twice-folded article is then discharged from the folding rolls onto delivery plate Ztl. The control system for the second folding means is generally identical to that for the first folding means except that the second fold timing means may use different circuit parameters.

FIGURE 2 illustrates the logic circuits and timing means contained within box 30 of FIGURE 1. The preferred timing means is an analog delayed pulse generator comprising a triode which is normally biased beyond cutoff by a negatively charged capacitor connected across grid and cathode; the logic circuit includes a timer reset gate which normally applies a capacitor charging and grid biasing potential to the grid of the triode; the slow time cycle initiating gate of the logic section connects a first resistance in shunt with the capacitor, the charging potential now being removed therefrom; the fast time cycle initiating gate connects a second resistance in shunt with the capacitor, said second resistance being one-half the value of the first. The grid potential will rise as a result of the discharge of the capacitor through the RC decay circuits thus formed, and when it exceeds the cutoff voltage the triode will become conducting; the plate current thereof flows through a relay coil, thereby causing a contact closure which may be used, directly or indirectly, to actuate the folding means. The length of the pulse delay is a function, inter alia, of the RC time constants, the cutoff potential of the particular triode used, and the initial gridrbiasing potential; the latter may be adjusted by means of a single potentiometer or voltage divider, thus afiording a simple, convenient and accurate means of calibrating the time of actuation of the folding blade in relation to cutoff voltage, system time lag and other initially indeterminate variables. Various modifications of, and equivalent devices for, the analog timing means will be discussed hereinbelow.

In FIGURE 2, all relay armatures are shown in their normal or deactivated position, i.e., no article is present in the article measuring zone. Switch 29' is a single pole-double throw switch operated by relay 29 of FIG- URE 1 (the forward sensor); switch 33 is a single polesingle throw switch operated by relay 33 of FIGURE 1 (the rear sensor) the respective relay coils for these switches have been omitted for the purpose of simplification-switches 29 and 33 may also be finger or pressure-type switches insofar as the essential invention herein is concerned. Relay 543 is the measuring cycle enabling relay and is provided with a single pole-double throw switch 51 and a coil 52 connected in series with the plate circuit of tube V Relay 53 is the timer enabling relay and is furnished with a pair of single pole-single throw switches 54 and 55 and a coil 56; switch 55 functions as a latching contact for relay 53. Relay 57 is the forward sensor relay and is provided with a coil 60, a single poledouble throw switch 58 and a single pole-single throw switch 5% the latter serving as a latching contact for relay 57. Relay fill is the rear sensor relay and comprises a double pole-double throw switch 62 and coil 63. Relay 64 is the output holding relay and contains a single pole-double throw switch 65 and a coil 66. A Voltage sufficient to operate the relays is applied to terminals L-1 and 'L-Z; an appropriate plate voltage for tube V is applied to the 13+ terminal; a negative grid biasing voltage E,; is connected across voltage divider R and an output pulse for actuating the folding means is taken from terminal L-3.

The time constant for the slow timing cycle is provided by (R +R )C and that for the fast timing cycle is provided by R the resistance of R is made equal to the resistance of R so that the slow period time constant, which we may designate as T is twice the fast period time constant T The circuit parameters are selected such that where D is the distance between points A and B of FIGURE 1 and v is the linear velocity of feed ribbons 11. Vernier adjustment of the total timer rundown period, and hence the location of the fold, is made by means of voltage divider R whereby the initial grid bias potential may be varied.

The operation of the invention may be more clearly understood by treating separately the folding of a short article (L D), an intermediate length article (L=D), and a long article (D L2D); in addition, the folding of successive, closely spaced articles will be separately considered.

I. Folding of a Short Article When the leading edge of a short article arrives at point A of FIGURE 1, switch 29' is activated. Coil 5d of relay 53 is energized via path (Lll)abcd-ground and is locked in via path (L-dl)abd5'6-ground. When the trailing edge of the article departs from point A, switch 29 is deactivated, relay d3 now being latched. Coil 69 of relay 57 is energized via path (L-ll)a-be-f-dllground and is locked in via path (Lll)abg6- ground. The series combination of resistors R and R is now connected in shunt with capacitor C via path hi-jR -R C and the slow timing cycle commences.

When the leading edge of the short article arrives at point B of FIGURE 1, switch 33' is activated. Coil 63 of relay 61 is energized via path (Li)kl-63-ground. Resistor R alone is now connected in shunt with capacitor C via path hz'mR C and the fast timing cycle commences.

Upon expiration of the timing period, tube V becomes conducting and coil 52 of relay Ed is energized whereby switch 51 is momentarily activated. Voltage from terminal L-l appears at output terminal L3 via path (L-l)a-n(L-3), and also energizes coil 66 of relay 64 via path (Ll)andd-ground. The activation of switch 51 releases the latching voltage from relays 53 and 57, effecting the deactivation of switches 54-, 55, 58 and 5%; and the activation of switch 65 of relay 6% de-energizes coil 63 of relay 61, effecting deactivation of switch 62. Grid biasing and capacitor charging voltage from voltage divider R is now applied to the grid of tube V via path R qp-h, which resets the timer by charging capacitor C and cutting off tube V Coil 52 of relay 5th is now tie-energized and switch 51 is deactivated.

It may be observed that the activation period of switch 51 is very short and depends on the switching time of relays 57, 64 and 61 and on the time required for capacitor C to be charged to cutoff potential. The output pulse appearing on terminal L-3 would normally be too short to operate the folding means. Relay 64 is therefore provided with latching contacts whereby coil 66 remains energized,

following the deactivation of switch 51, via path (Li) k-fidground. The output pulse is maintained at terminal 1P3 via path (L-ll)k-n-(L3) until switch 33' should become deactivated, which event occurs when the trailing edge of the article departs from point B of FIGURE 1. When switch 33' opens, relay 64 is deenergized and all switching elements are now returned to their initial state, assuming for the moment that a succeeding article has not yet arrived at point A of FIGURE 1.

In the event that the output pulse is too long to permit satisfactory operation of air piston 13, such pulse may be shortened by means of an electric or pneumatic cutoif 10 relay inserted between terminal L-3 and solenoid valve 42.

As above noted, air piston 13 is actuated when the midlength of article 12 is opposite point C, the forward displacement of which from folding blade 14 compensates for the response time of the folding means. In some cases, point C may be identical with rear sensing point B; but more often than not, space considerations require that point C be displaced from point B a distance K, which need only be a few inches at most. The minimum length of an article which can be measured by the instant apparatus must be equal to or greater than 2K, since the rear sensor must remain activated at least until relay 50 is energized.

An examination of the mathematics of the timing circuit will serve to demonstrate its operation more clearly. In this regard, the following symbols are defined:

t =time duration of slow timing cycle t =time duration of fast timing cycle e =initial grid bias voltage (negative) at zero time e =cutolf voltage of triode V D=distance between points A and B K=distance between points B and C L=length of article between limits of 2K and 2D v=velocity of article (constant) T =(R +R )C =D/v, the slow period time constant T =R C =D/2v, the fast period time constant G=natural logarithm base The general equation for the timing circuit, including both slow and fast timing cycles, is given by:

The initial grid bias voltage c is adjusted so that the rnid length of an article of length L equal to 2D will be opposite point C when e has decayed to e The slow timing cycle commences when the leading edge of the long article reaches rear sensing point B, and the fast timing cycle commences when the midlength thereof reaches point B (its trailing edge then leaving point A.). The fast timing cycle must expire when the midlength reaches point C. Therefore,

Equations 1, 2 and 3 are valid for articles of any length between the limits of 2K and 2D (2KL2D).

For a short article (2KL D), the slow timing cycle commences when the trailing edge thereof passes point A, and the fast timing cycle commences when the leading edge thereof reaches point B. The duration of the slow timing cycle is therefore given by:

Substituting this value in Equation 3, we have K L w n The distance traveled by the leading edge of the article during t is equal to vi or K+L/ 2, which places the midlength of the article opposite point C upon expiration of the fast timing cycle.

II. Folding of an Intermediate Length Article When the leading edge of an article of intermediate length (L'=D) arrives at point A of FIGURE 1, switch 29' is activated. Coil 56 of relay 53 is energized via path (L-1)-a-b-c-56-ground and is locked in via path (L-li)- a-b-d-Sfi-ground. When the trailing edge of the article departs from point A, the leading edge simultaneously reaches point B so that switch 29 is deactivated and switch 33 is concurrently activated. Coil 60 of relay 57 is energized via path (L-l)ab-e-f6-ground and is locked in via path (L-1)-abg6tl-ground; coil 63 of relay 61 is energized via path (L-l)kl-63-ground. Resistor R is connected in shunt with capacitor C via path him-R -C and the timer starts immediately in its fast timing cycle, bypassing the slow timing cycle altogether. The remaining sequence of operations is the same as for a short article, described above.

Since in this case the duration of the slow timing cycle t is zero, we have from Equation 3, supra,

r a 2- 2v v 2v The fast timing cycle commences when the leading edge of the article reaches point B. The distance traveled by the leading edge during t is equal to vi or which places the midlength of the article opposite point C upon expiration of the fast timing cycle.

III. Folding of a Long Article When the leading edge of a long article (D L2D) arrives at point A of FIGURE 1, switch 29' is activated. Coil 56 of relay 53 is energized via path (L1)a-be 56-ground and is locked in via path (L-1)-a-b-d-56- ground. When the leading edge of the article reaches point B, switch 33 is activated, thereby energizing coil 63 of relay 61 via path (L1)kl-63-ground. The series combination of resistors R and R is now connected in shunt with capacitor C via path hp, 'R R C and the slow timing cycle commences.

When the trailing edge of the long article departs from point A of FIGURE 1, switch 29' is deactivated, relay 53 now being latched. Coil 60 of relay 57 is energized via path (L1)-abe-f60-ground and is locked in via path (L1)-a-b-g-60 ground. Resistor R alone is now connected in shunt with capacitor C via path himR C and the fast timing cycle commences. The remaining sequence of operations is the same as for a short article, described above.

For a long article (D L2D), the slow timing cycle commences when the leading edge thereof reaches point B, and the fast timing cycle commences when the trailing edge thereof departs from point A. The duration of the slow timing cycle is therefore given by:

Substituting this value in Equation 3, supra, we have D L K The distance traveled by the trailing edge of the article during t is equal to vt or which places the midlength of the article opposite point C upon expiration of the fast timing cycle.

IV. Folding Two or More Closely Spaced Articles The passage of a first short article into the article measuring zone defined by sensing points A and B will activate switch 29 and will then deactivate switch 29 prior to activation of switch 33'; relays 53 and 57 are energized and latched as previously described, and the serial combination of resistors R and R is shunted across capacitor C via path hi 'R R C A second article may now cross point A without disrupting the slow time cycle presently taking place for the first article: the reactivation of switch 29 at this time will not cause relay 57 to drop out because it is latched in by contact 59. 7

However, the spacing between articles and the lengths thereof must be sufliciently great so that the fast time cycle for the first article is completed, and the timing circuit reset, before the trailing edge of the second article passes point A, otherwise the slow time period for the second article will not be initiated at the proper time. The same considerations apply where the first article is long. Neglecting the very small delays imposed by the relay switching times, the relationship is expressed by:

dmi. D +1) where d is the minimum spacing between articles, L is the length of the first article and L is the length of the second article. By way of example, if D is 60 inches, L is 30 inches and L is 40 inches, then the spacing must be greater than 5 inches; however, if L and L both exceed 40 inches, then the spacing may be substantially zero.

By way of comparison, the spacing requirement for a conventional single sensing point system is given by If D is 60 inches and L is 40 inches, then the minimum spacing must be greater than 40 inches. The reduced piece rate capacity and hence the need for a plurality of standby timing mechanisms is at once apparent.

Various alternative embodiments of the present invention will suggest themselves to those skilled in the machine control and computer arts. With regard to the timing means, any suitable voltage sensitive gating element may be substituted for the Vacuum triode, such as, for example, a vacuum tube having two or more grids, a thyratron, a transistor, etc. Where the controller for the second folding means is unitarily constructed with the first fold controller, the triodes for the two timing circuits may be advantageously integrated in a single envelope, as by employing a double triode, and may share a common power supply. The two RC time constants may be obtained in several ways, as by using a single resistor and switching two capacitors, or by using two or more resistors and capacitors, or by separately shunting either of two resistors across a capacitor. The inverse of the delayed pulse generator circuit affords another form of analog timing means, that is, relay 50 may be normally energized and the grid of the triode normally maintained above cutoff; the slow speed and high speed timer initiating gating means would then be operative to apply a negative biasing voltage to the grid through different RC decay circuits whereby de-energization of relay 50 would then signify completion of the timing period.

In addition to analog timing means, it is within the scope of the present invention to substitute mechanical or digital timing means therefor. A suitable mechanical timer may comprise a cam-actuated switching means driven by a low speed motor and a high speed motor, each through an overrunning clutch means. A suitable digital timer may comprise a binary time gate counter receiving pulses from a fixed frequency clock pulse source, the input logic thereof being arranged to count one bit/pulse during the slow timing period and 2 bits/pulse during the fast timing period; the time gate counter may be provided with rotary selector switch readout to a multi-input AND gate, the output of which, when true,

13 signifies completion of the counting period. Alternatively, a digital tachometer linked to the folding machine drive motor could be substituted for the constant frequency clock, in which case direct synchronization of feed ribbon speed with the timing means may be accomplished.

It is also within the scope of this invention to substitute electronic or magnetic logic elements-vacuum tube or solid state-for any or all of the relay switching elements shown in FIGURE 2. For example, latching relays 53, '7 and 64 may be replaced with flip flops, two or more contacts in series with a diode AND gate, two or more contacts in parallel with a diode OR gate, etc.

Although primarily adapted for use with laundry folding machines, the present apparatus finds utility in other applications wherein it is desired to locate the midlength of a moving object of unknown length; exemplary services include the rolling, stamping or bending of metal by automatic metal-working lines, the manufacturing of boxes, cartons and food packages, and the size reduction of raw timber.

I claim as my invention:

1. Apparatus for locating the midlength of an article moving at constant velocity in a direction parallel to its length which comprises in combination: a forward article presence sensor and a rear article presence sensor, each of which sensors is activated so long as said article overlaps a corresponding fixed sensing point and is otherwise deactivated, said sensing points being spaced from each other in the direction of movement of said article, a dual speed timing means having a slow timing cycle and a fast timing cycle, a first gating means initiating said slow timing cycle in response to initial activation of said forward sensor and subsequent occurrence of either of two events consisting of (a) deactivation of said forward sensor and (1)) activation of said rear sensor, a second gating means initiating said fast timing cycle in response conjunctively to initial activation of said forward sensor and subsequent occurrence of both the deactivation of said forward sensor and the activation of said rear sensor, and an output switching element operatively connected to said timing means and changing state upon termination of its timing period.

2. Apparatus for locating the midlength of an article moving at constant velocity in a direction parallel to its length comprising a forward article presence sensor and a rear article presence sensor, each of which sensors is activated so long as said article overlaps a corresponding fixed sensing point and is otherwise deactivated, said sensing points being spaced from each other in the direction of movement of said article, a dual speed timing means having a slow timing cycle and a fast timing cycle, a first gating means initiating said slow timing cycle in response to initial activation of said forward sensor and subsequent occurrence of either of two events consisting of (a) deactivation of said forward sensor and (b) activation of said rear sensor, a second gating means initiating said fast timing cycle in response conjunctively to initial activation of said forward sensor and subsequent occurrence of both the deactivation of said forward sensor and the activation of said rear sensor, an output switching element operatively connected to said timing means and changing state upon termination of its timing period, and means for resetting said timing means immediately responsive to said change of state of said output switching element.

3. The apparatus of claim 2 further characterized in the provision of a bistable storage element operatively connected to said output switching element and changing state responsive to change of state of the latter.

4. Apparatus for locating the midlength of an article moving at constant velocity in a direction parallel to its length which comprises in combination: a forward article presence sensor and a rear article presence sensor, each of which sensors is activated so long as said article overlaps a corresponding fixed sensing point and is otherwise deactivated, said sensing points being spaced from each other in the direction of movement of said article, a dual period delayed pulse generator having a slow period and a fast period, a first gating means initiating said slow period in response to initial activation of said forward sensor and subsequent occurrence of either of two events consisting of (a) deactivation of said forward sensor and ([1) activation of said rear sensor, a second gating means initiating said fast period in response conjunctively to initial activation of said forward sensor and subsequent occurrence of both the deactivation of said forward sensor and the activation of said rear sensor, and an output switching element operatively connected to said pulse generator and changing state upon generation of a pulse therefrom.

5. The apparatus of claim 4 further characterized in that said delayed pulse generator comprises a voltagesensitive gating element normally biased beyond cutoff by capacitor means, said first and second gating means connecting different resistances in shunt with said capacitor means.

6. The apparatus of claim 5 further characterized in the provision of a source of adjustable biasing voltage and switching means applying said biasing voltage to said capacitor means immediately responsive to generation of said pulse.

7. The apparatus of claim 6 further characterized in the provision of means for removing all shunt resistance from said capacitor means immediately responsive to generation of said pulse.

8. Apparatus for locating the midlength of an article moving at constant velocity v in a direction parallel to its length which comprises in combination: a forward article presence sensor and a rear article presence sensor, each of which sensors is activated so long as said article overlaps a corresponding fixed sensing point and is otherwise deactivated, said sensing points being spaced apart from each other a distance D in the direction of movement of said article, a voltage-sensitive gating element normally biased beyond cutofi? by capacitor means, a first gating means connecting a first resistance in shunt with said capacitor means in response to initial activation of said forward sensor and subsequent occurrence of either of two events consisting of (a) deactivation of said forward sensor and (1)) activation of said rear sensor, a second gating means connecting a second resistance in shunt with said capacitor means in response conjunctively to initial activation of said forward sensor and subsequent occurrence of both the deactivation of said forward sensor and the activation of said rear sensor, the RC time constant provided by said first gating means being substantially twice the RC time constant provided by said second gating means, and an output switching element operatively connected to said voltage-sensitive gating element and changing state upon activation of the latter, corresponding to the alignment of the midlength of said article with a fixed reference point in its path of travel.

9. The apparatus of claim 8 further characterized in that said first gating means provides a time constant T equal to D/v and said second gating means provides a time constant T equal to D/ 2v.

10. Apparatus for locating the midlength of an article moving at constant velocity in a direction parallel to its length which comprises in combination: a forward article presence sensor and a rear article presence sensor, each of which sensors is activated so long as said article overlaps a corresponding fixed sensing point and is otherwise deactivated, said sensing points being spaced from each other in the direction of movement of said article, a dual speed timing means having a slow timing cycle and a fast timing cycle, a measuring cycle enabling gate, a timer enabling storage element responsive to deactivation of said enabling gate and activation of said forward sensor, a slow time cycle initiating gate responsive to activation of said timer enabling storage element and subsequent occurrence of either of two events consisting of (a) deactivation of said forward sensor and ([1) activation of said rear sensor, a fast time cycle initiating gate responsive conjunctively to activation of said timer enabling storage element and subsequent occurrence of both the deactivation of said forward sensor and the activation of said rear sensor, said measuring cycle enabling gate being activated by said timing means upon termination of its timing period.

11. The apparatus of claim 10 further characterized in the provision of an output storage element which is activated in response conjunctively to activation of said rear sensor and said measuring cycle enabling gate and is deactivated by subsequent deactivation of said rear sensor.

12. Apparatus for locating the rnidlength of an article moving at constant velocity in a direction parallel to its length which comprises in combination: a forward article presence sensor and a rear article presence sensor, each of which sensors is activated so long as said article overlaps a corresponding fixed sensing point and is otherwise deactivated, said sensing points being spaced from each other in the direction of movement of said article, a dual speed timing means having a slow timing cycle and a fast timing cycle, a normally deactivated measuring cycle enabling gate which is activated by said timing means upon termination of its timing period, a timer enabling storage element responsive conjunctively to deactivation of said enabling gate and activation of said forward sensor, a forward sensor storage element responsive conjunctively to deactivation of both said enabling gate and said forward sensor and to activation of said enabling storage element, an output storage element responsive conjunctively to activation of both said rear sensor and said enabling gate, a rear sensor gate responsive conjunctively to activation of said rear sensor and deactiva tion of said output storage element, a slow time cycle initiating gate responsive to either of two sets of conditions consisting of (a) activation of said forward sensor storage element coupled with deactivation of said rear sensor gate and (b) deactivation of said forward sensor storage element coupled with activation of said rear sensor gate, a fast time cycle initiating gate responsive conjunctively to activation of both said forward sensor storage element and said rear sensor gate, the activation of said measuring cycle enabling gate effecting the concurrent deactivation of said timer enabling storage element and said forward sensor storage element and the deactivation of said rear sensor effecting the deactivation of said output storage element. 7

13. The apparatus of claim 12 further characterized in the provision of a timing means reset gate responsive conjunctively to the deactivation of both said forward sensor storage element and said rear sensor gate.

References Cited in the file of this patent UNITED STATES PATENTS 2,374,779 Preston May 1, 1945 2,516,454 Doran July 25, 1950 3,071,711 Hunter Jan. 1, 1963 

2. APPARATUS FOR LOCATING THE MIDLENGTH OF AN ARTICLE MOVING AT CONSTANT VELOCITY IN A DIRECTION PARALLEL TO ITS LENGTH COMPRISING A FORWARD ARTICLE PRESENCE SENSOR AND A REAR ARTICLE PRESENCE SENSOR, EACH OF WHICH SENSORS IS ACTIVATED SO LONG AS SAID ARTICLE OVERLAPS A CORRESPONDING FIXED SENSING POINT AND IS OTHERWISE DEACTIVATED, SAID SENSING POINTS BEING SPACED FROM EACH OTHER IN THE DIRECTION OF MOVEMENT OF SAID ARTICLE, A DUAL SPEED TIMING MEANS HAVING A SLOW TIMING CYCLE AND A FAST TIMING CYCLE, A FIRST GATING MEANS INITIATING SAID SLOW TIMING CYCLE IN RESPONSE TO INITIAL ACTIVATION OF SAID FORWARD SENSOR AND SUBSEQUENT OCCURRENCE OF EITHER OF TWO EVENTS CONSISTING OF (A) DEACTIVATION OF SAID FORWARD SENSOR AND (B) ACTIVATION OF SAID REAR SENSOR, A SECOND GATING MEANS INITIATING SAID FAST TIMING CYCLE IN RESPONSE CONJUNCTIVELY TO INITIAL ACTIVATION OF SAID FORWARD SENSOR AND SUBSEQUENT OCCURRENCE OF BOTH THE DEACTIVATION OF SAID FORWARD SENSOR AND THE ACTIVATION OF SAID REAR SENSOR, AN OUTPUT SWITCHING ELEMENT OPERATIVELY CONNECTED TO SAID TIMING MEANS AND CHANGING STATE UPON TERMINATION OF ITS TIMING PERIOD, AND MEANS FOR RESETTING SAID TIMING MEANS IMMEDIATELY RESPONSIVE TO SAID CHANGE OF STATE OF SAID OUTPUT SWITCHING ELEMENT. 